1. Field of the Invention
The present invention relates to a display device. In particular, the invention relates to a circuit configuration for driving scan lines or data lines of pixels in an active matrix display device which includes light-emitting elements.
2. Description of the Related Art
In recent years, further development of thin displays has been advanced in response to the growing demand for applications of thin displays to mainly television sets, computer monitors, mobile terminals, and the like. As a thin display, there are a liquid crystal display device (LCD) and a display device having light-emitting elements. In particular, an active matrix display using light-emitting elements is expected as the next-generation display because not only can it achieve a thin-shape, lightweight, and high-definition display, and the like which are the same features as those of the existing LCDs, but also it has advantages such as a high response speed, wide viewing angles, and the like.
As the most basic pixel configuration of an active matrix display using light-emitting elements, a configuration shown in FIG. 11A can be given as an example (for example, see Japanese Patent No. 3620538). The pixel shown in FIG. 11A includes a driving transistor 2402 for controlling a current supply to a light-emitting element 2404, a switching transistor 2401 for delivering a potential of a data line 2406 to a gate node G of the driving transistor 2402 when the pixel is selected by a scan line 2405, and a storage capacitor 2403 for holding a potential of the node G One electrode of the storage capacitor 2403 and one of a source electrode and a drain electrode of the driving transistor 2402 are connected to a current supply line 2407. The other of the source electrode and the drain electrode of the driving transistor 2402 is connected to a counter electrode 2408 through the light-emitting element 2404. FIG. 11B shows an example of the signal timing of the scan line 2405, the data line 2406, and the node G.
As a method for expressing gray scales, there are an analog driving method and a digital driving method. In the analog driving method, an analog voltage is supplied to a gate of a driving transistor so that the value of a current supplied to a light-emitting element is changed in an analog manner. On the other hand, in the digital driving method, one of two signal values for selecting light emission or non-light emission of a light-emitting element is supplied to a gate of a driving transistor, and the luminance level of the light-emitting element is fixed in the whole light-emitting time, so that gray scales are expressed by controlling the length of the light-emitting time of the light-emitting element.